Field of the Invention
The present invention relates to moisture free transport of materials, and particularly polymer materials.
Description of the Related Art
A saponified ethylene-vinyl ester-based copolymer (ethylene-vinyl alcohol-based copolymer resin; which is referred to hereinafter as an “EVOH resin”) has a very strong intermolecular force because of the hydrogen bonding of hydroxyl groups present in polymer side chains. Accordingly, films made of the EVOH resin exhibit excellent gas barrier properties. For this reason, the EVOH resin (and “EVOH resin pellets” obtained by pelletizing the EVOH resin) is used for packaging films and packaging container raw materials for water, foods, drinks and the like, and for films and sheets of medical product packaging materials, industrial chemical packaging materials, agricultural chemical packaging materials and the like, or as a molding material for containers such as bottles (as disclosed in Japanese Published Patent Application No. 2011-6673, the disclosure of which is herein incorporated by reference).
In general, the EVOH resin is produced by saponifying an ethylene-vinyl ester-based copolymer in an alcohol solvent in the presence of a catalyst under high-temperature and high-pressure conditions, the ethylene-vinyl ester-based copolymer being obtained by the copolymerization of a fatty acid vinyl ester such as vinyl acetate and ethylene. The EVOH alcohol solution under high-temperature and high-pressure conditions which is obtained in such a saponifying step shall be a water/alcohol mixed solution of EVOH stable at ordinary pressure, and is extruded into a low-temperature coagulating bath having water as a main ingredient so as to be precipitated in the form of strands. The strands are cut, pelletized, and then dried, so that EVOH resin pellets are produced.
The EVOH resin (pellets) has hygroscopic properties. It has been known that, if the EVOH resin (pellets) absorbs moisture to increase the moisture percentage (percentage of moisture content) thereof when in storage, the EVOH resin (pellets) is prone to have a poor appearance resulting from the foaming of moisture and the like during a subsequent molding process of films and the like. To prevent this, the aforementioned EVOH resin, if small in quantity (approximately 25 kg or less), is charged and enclosed in transporting bags having an aluminum layer impervious to moisture when transported in the form of pellets between plants or to a customer or stored therein.
In the case of a large-scale step or plant in which the EVOH resin pellets are used in large quantities in a short time, on the other hand, the use of the transporting bags for small quantities as described above for the transport and storage of the pellets results in the decrease in transporting and operating efficiencies. When the EVOH resin pellets are required in large quantities at one time, it is customary to charge the aforementioned EVOH resin pellets in large-scale closed containers (pellet transport containers) such as large-sized tanks, hoppers and containers, to close the containers, and to transport the containers containing the EVOH resin pellets by using towing vehicles, trains and the like.
For actual transport, storage tank parts of trucks in the form of a trailer (including a large-sized bulk loading vehicle for granules towed by a tractor, such as a semi-trailer and a full trailer) in which a tank for powder and granular materials, a hopper and the like are fixed (normally provided) on a bed (frame), and in the form of a tank truck integrated with a tractor part, and the like are used as large-scale closed containers capable of loading pellets (coarse granules) thereon, as pellet transport containers.
When a large-sized pellet transport container (air closed tank of a trailer for granules, a bulk vehicle and the like) as described above is used to transport EVOH resin pellets, the pellets which remain at a high temperature (hot) after being subjected to hot air drying in the final stage of the manufacturing process thereof are charged into the aforementioned closed tank and transported, with the openings of the tank sealed, for the purpose of avoiding the moisture absorption of the pellets during the transport and storage of the pellets. It has, however, been found that the method of transporting the EVOH resin pellets in the aforementioned manner might cause the aforementioned pellets to absorb moisture during the transport thereof.
As a result of the detailed observation of the state of the pellet transport container being transported, the present inventors have found that, as the temperature of gas within the container which has increased by the charging of the aforementioned hot pellets decreases during the transport of the pellets, a negative pressure resulting from heat shrinkage is developed, so that outside air enters the container. From this fact, it is considered that the moisture absorbed by the aforementioned EVOH resin pellets is brought about by the outside air containing much moisture and coming from the outside of the pellet transport container (closed tank).
There is a danger that such moisture absorption of the EVOH resin pellets during the transport of the EVOH resin pellets causes the occurrence of a large number of failures or poor appearances resulting from the foaming of moisture and the like during the molding process of films and the like. It is therefore desirable to improve the mass transport method of the EVOH resin pellets.